This invention is directed to an improved rotary hydraulic machine and more particularly relates to a rotary pump/turbine, hereinafter referred to as a pump, wherein energy losses due to fluid friction are reduced by introducing into spaces defined between the rotor and the housing a fluid of less density and viscosity than the working or pumped fluid.
In conventional rotary or centrifugal pumps, a rotating rotor or impeller within a stationary housing is used to impart energy to the pumped fluid wherein a relatively small space defined between the rotating element and the housing often becomes filled with the pumped fluid. Energy losses dissipated through shearing of the pumped fluid in such spaces can amount to as much as twelve percent or more of the total power input, depending upon the type and design of the pump. Such frictional power loss caused by shearing of the fluid is generally set forth by the relationship, power loss=KD.sup.2 du.sup.3 wherein K is a numerical coefficient dependent upon the Reynolds number, rotor surface finish, and rotor to housing clearance; D is the rotor diameter; d is the fluid density; and u is the peripheral velocity of the rotor. Attempts made to minimize such power losses include optimizing the clearance between the rotor and the housing as well as polishing or coating adjacent portions of the rotor and housing to obtain surfaces having a lower effective friction coefficient. Another proposal involves the installation of one or more free-rotating disks between the rotor and casing wherein such rotating disks reduce the relative velocity differential between the rotating and stationary boundaries, thus reducing friction losses therebetween.
Further attempts to reduce fluid friction have involved the substitution of a fluid of less density and lower viscosity than the pumped fluid in the spaces between the rotor and the housing. As exemplified by U.S. Pat. Nos. 3,044,744 and 3,172,640, for example, air is introduced into spaces between the rotor and housing surfaces. Additionally, U.S. Pat. Nos. 3,174,719; 3,188,050; 3,236,499; 3,405,913; 3,635,582; and 3,724,966 effect sealing of the aerated spaces by establishing and maintaining water and/or labyrinth seals to prevent excessive losses of the air or gas used in such spaces. Recognizing that reasonable prevention of gas or air loss in the aerated spaces requires seals of substantial effective width and that fluid friction losses at a runner seal vary as the 4th power of the diameter, the width and clearance tolerances as well as the relative position of such seals in the pump structures of the type in the aforementioned patents has been the subject of much investigation. However, the need for continuous supervision of the supply of sealing fluid to the seal structures and the close operating tolerances of the labyrinth seals, for example, provides many inherent disadvantages and limitations on the use of such seal structures. Additionally, the seal structures of the prior art are generally not readily adaptable to either the condition wherein a gas of varying temperature and pressure is used or wherein sizeable pressure differentials exist between the pumped fluid and the annular spaces between the rotor and the housing. Accordingly, the structure of the present invention is designed to overcome disadvantages of the prior art, such as varying pressure differentials between the pumped fluid and the aerated spaces which results in intermittent seal loss.